SPECIATION OF ARSENIC(V) AND ARSENIC(III) BY CATHODIC STRIPPING VOLTAMMETRY IN FRESH-WATER SAMPLES

A voltammetric stripping procedure is described for the determination of arsenic(V) in a mannitol-sulphuric acid medium. The arsenic is copr ecipitated with copper and selenium and reduced to arsine at the hangi ng mercury drop electrode. Using an accumulation time of 240 s, the de tection limit is 0.52 mu g L-1, the determination limit is 0.9 mu g L- 1. The method has been applied to the determination of arsenic in wate r samples. By varying the composition of the supporting electrolyte it is possible to differentiate between arsenic(III) and arsenic(V). As both oxidation states have different toxicological characteristics, th e ability to discriminate between both is an distinct advantage of the proposed method.